Geon-Young Kim

Structural properties in flame quenched Cu−9Al−4.5Ni−4.5Fe alloy

The flame quenching process has been employed to modify the surfaces of a commercial marine propeller material, aluminum bronze alloy (Cu−9Al−5Ni−5Fe), and the material’s microstructure and hardness properties have been studied. The thermal history was accurately monitored during the process at various surface temperatures and holding times. XRD and EDX analyses have shown that aboveTβ temperature the microstructure consisting of α and κ phases changes into α and β’ martensite due to an eutectoid reaction of α+β→κ and a martensitic transformation of β→β’. The β’ martensite phase formed has a face-centered cubic (FCC) crystal structure with typical twinned structure. The hardness of the flame-quenched layer having the α+β’ structure is similar to or lower than that of the α+κ structure, depending highly on the size and distribution of β’ and κ phases. It is noted that the sliding wear resistance of the flame-quenched layer is enhanced with the formation of β’ martensite.

Thermal Conductivity Estimation of Compacted Bentonite Buffer Materials for a High-Level Radioactive Waste Repository

Abstract A deep geological repository has been considered as one of the most appropriate options for the disposal of high-level radioactive waste (HLW), and it will be constructed in a host rock area at a depth of 500 to 1000 m below the ground surface. The geological repository system is based on the concept of an engineered barrier system, and it consists of a disposal canister with packed spent fuel, buffer material, backfill material, and intact rock. The buffer plays an important role to assure the disposal safety of HLW since it can restrain the release of radionuclides and protect the canister from the inflow of groundwater. Since an increased heat quantity is released from the disposal canister into the surrounding buffer material, the thermal conductivity of the buffer material constitutes a key parameter needed to analyze the entire disposal safety. Therefore, this study presents a thermal conductivity prediction model for compacted bentonite buffer material from Kyungju, which is the only bentonite produced in Korea. The thermal conductivity of the compacted bentonite buffer from Kyungju was measured using a hot-wire method according to varying degrees of saturation, dry density, and temperature. The measurements showed that the thermal conductivity was concurrently influenced by the degree of saturation, dry density, and temperature variation. A regression model was proposed to predict the thermal conductivity of the compacted bentonite buffer from Kyungju using the degree of saturation and the dry density as the dependent variables. An additional regression model was also introduced that incorporated the temperature variation as an additional dependent variable, and the two models were directly compared with each other.